汽车制动系统英文文献及翻译Word文档下载推荐.docx

1、 Mechanical advantage （leverage） Hydraulic force multiplication The brakes transmit the force to the tires using friction, and the tires transmit that force to the road using friction also. Before we begin our discussion on the components of the brake system， well cover these three principles:Levera

2、ge Hydraulics Friction Leverage and HydraulicsIn the figure below, a force F is being applied to the left end of the lever. The left end of the lever is twice as long （2X） as the right end （X）. Therefore, on the right end of the lever a force of 2F is available， but it acts through half of the dista

3、nce （Y） that the left end moves （2Y）。 Changing the relative lengths of the left and right ends of the lever changes the multipliers。 The pedal is designed in such a way that it can multiply the force from your leg several times before any force is even transmitted to the brake fluid. The basic idea

4、behind any hydraulic system is very simple: Force applied at one point is transmitted to another point using an incompressible fluid， almost always an oil of some sort。 Most brake systems also multiply the force in the process。 Here you can see the simplest possible hydraulic system:Your browser doe

5、s not support JavaScript or it is disabled. Simple hydraulic system In the figure above， two pistons （shown in red） are fit into two glass cylinders filled with oil （shown in light blue） and connected to one another with an oil-filled pipe。 If you apply a downward force to one piston （the left one，

6、in this drawing）， then the force is transmitted to the second piston through the oil in the pipe. Since oil is incompressible, the efficiency is very good almost all of the applied force appears at the second piston. The great thing about hydraulic systems is that the pipe connecting the two cylinde

7、rs can be any length and shape， allowing it to snake through all sorts of things separating the two pistons. The pipe can also fork, so that one master cylinder can drive more than one slave cylinder if desired， as shown in here：Your browser does not support JavaScript or it is disabled。Master cylin

8、der with two slaves The other neat thing about a hydraulic system is that it makes force multiplication （or division） fairly easy。 If you have read How a Block and Tackle Works or How Gear Ratios Work， then you know that trading force for distance is very common in mechanical systems. In a hydraulic

9、 system, all you have to do is change the size of one piston and cylinder relative to the other, as shown here：Hydraulic multiplication To determine the multiplication factor in the figure above， start by looking at the size of the pistons。 Assume that the piston on the left is 2 inches （5。08 cm） in

10、 diameter （1-inch / 2.54 cm radius）, while the piston on the right is 6 inches （15.24 cm） in diameter （3inch / 7.62 cm radius）. The area of the two pistons is Pi * r2. The area of the left piston is therefore 3。14, while the area of the piston on the right is 28.26。 The piston on the right is nine t

11、imes larger than the piston on the left。 This means that any force applied to the lefthand piston will come out nine times greater on the right-hand piston。 So, if you apply a 100-pound downward force to the left piston， a 900pound upward force will appear on the right. The only catch is that you wi

12、ll have to depress the left piston 9 inches （22.86 cm） to raise the right piston 1 inch （2。54 cm）.A Simple Brake SystemBefore we get into all the parts of an actual car brake system, lets look at a simplified system：A simple brake system You can see that the distance from the pedal to the pivot is f

13、our times the distance from the cylinder to the pivot， so the force at the pedal will be increased by a factor of four before it is transmitted to the cylinder. You can also see that the diameter of the brake cylinder is three times the diameter of the pedal cylinder. This further multiplies the for

14、ce by nine。 All together, this system increases the force of your foot by a factor of 36。 If you put 10 pounds of force on the pedal, 360 pounds （162 kg） will be generated at the wheel squeezing the brake pads。There are a couple of problems with this simple system。 What if we have a leak？ If it is a

15、 slow leak， eventually there will not be enough fluid left to fill the brake cylinder， and the brakes will not function. If it is a major leak, then the first time you apply the brakes all of the fluid will squirt out the leak and you will have complete brake failure。Drum brakes work on the same pri

16、nciple as disc brakes： Shoes press against a spinning surface。 In this system， that surface is called a drum.Figure 1. Location of drum brakes. See more drum brake pictures。Many cars have drum brakes on the rear wheels and disc brakes on the front。 Drum brakes have more parts than disc brakes and ar

17、e harder to service, but they are less expensive to manufacture， and they easily incorporate an emergency brake mechanism. In this edition of HowStuffWorks, we will learn exactly how a drum brake system works， examine the emergency brake setup and find out what kind of servicing drum brakes need. Fi

18、gure 2. Drum brake with drum in placeFigure 3. Drum brake without drum in placeLets start with the basics。The Drum BrakeThe drum brake may look complicated, and it can be pretty intimidating when you open one up. Lets break it down and explain what each piece does。Figure 4. Parts of a drum brakeLike

19、 the disc brake, the drum brake has two brake shoes and a piston。 But the drum brake also has an adjuster mechanism， an emergency brake mechanism and lots of springs。First, the basics: Figure 5 shows only the parts that provide stopping power. Figure 5。 Drum brake in operation When you hit the brake

20、 pedal， the piston pushes the brake shoes against the drum. Thats pretty straightforward， but why do we need all of those springs?This is where it gets a little more complicated. Many drum brakes are self-actuating。 Figure 5 shows that as the brake shoes contact the drum， there is a kind of wedging

21、action, which has the effect of pressing the shoes into the drum with more force。The extra braking force provided by the wedging action allows drum brakes to use a smaller piston than disc brakes. But， because of the wedging action, the shoes must be pulled away from the drum when the brakes are rel

22、eased. This is the reason for some of the springs. Other springs help hold the brake shoes in place and return the adjuster arm after it actuates. Brake AdjusterFor the drum brakes to function correctly, the brake shoes must remain close to the drum without touching it。 If they get too far away from

23、 the drum （as the shoes wear down， for instance）, the piston will require more fluid to travel that distance, and your brake pedal will sink closer to the floor when you apply the brakes。 This is why most drum brakes have an automatic adjuster. Figure 6. Adjuster mechanismNow lets add in the parts o

24、f the adjuster mechanism。 The adjuster uses the self-actuation principle we discussed above。Figure 7. Drum brake adjuster in operation In Figure 7， you can see that as the pad wears down, more space will form between the shoe and the drum。 Each time the car stops while in reverse, the shoe is pulled

25、 tight against the drum. When the gap gets big enough, the adjusting lever rocks enough to advance the adjuster gear by one tooth。 The adjuster has threads on it, like a bolt, so that it unscrews a little bit when it turns， lengthening to fill in the gap。 When the brake shoes wear a little more， the

26、 adjuster can advance again， so it always keeps the shoes close to the drum。Some cars have an adjuster that is actuated when the emergency brake is applied. This type of adjuster can come out of adjustment if the emergency brake is not used for long periods of time. So if you have this type of adjus

27、ter, you should apply your emergency brake at least once a week。ServicingThe most common service required for drum brakes is changing the brake shoes. Some drum brakes provide an inspection hole on the back side， where you can see how much material is left on the shoe。 Brake shoes should be replaced

28、 when the friction material has worn down to within 1/32 inch （0。8 mm） of the rivets。 If the friction material is bonded to the backing plate （no rivets）， then the shoes should be replaced when they have only 1/16 inch （1.6 mm） of material left. Photo courtesy of a local AutoZone storeFigure 9. Brak

29、e shoeJust as in disc brakes, deep scores sometimes get worn into brake drums。 If a wornout brake shoe is used for too long, the rivets that hold the friction material to the backing can wear grooves into the drum. A badly scored drum can sometimes be repaired by refinishing. Where disc brakes have a minimum allowable thickness， drum brakes have a maximum allowable diameter。 Since the contact surface is the inside of the drum, as you remove material from the drum brake the diameter gets bigger. Figure 10. Brak